1. Technical Field
The present disclosure relates to a component that provide electric conduction. More specifically, a terminal that connects electric wires, a method of manufacturing thereof, and a wire connecting structure that joins a terminal and an electric wire.
2. Background
In the related art, a connection between an electric wire and a terminal in an automotive wire harness or the like is generally a crimp connection in which an electric wire is crimped with a terminal which is referred to an open barrel type. However, with an open barrel type terminal, when moisture or the like comes into contact with a connecting part (contact point) between the electric wire and the terminal, oxidation of a metal surface of the electric wire and/or the terminal progresses, and an electric resistance at a connecting part will increase. When metals used for the electric wire and the terminal are different from each other, galvanic corrosion progresses. Progression of metal oxidation and corrosion at the connecting part causes a crack and a poor contact at the connecting part, and an influence on a product life cannot be avoided. Particularly, in recent years, wire harnesses having an electric wire made of an aluminum alloy and a terminal base material made of a copper alloy are put to practical use, and thus problems of oxidation and corrosion of the connection part are becoming more prominent.
In order to prevent corrosion of an aluminum wire at the connecting part, Japanese Laid-Open Patent Publication No. JP 2004-199934 discloses that the terminal is made of an aluminum alloy of the same material type as that of a wire conductor to suppress galvanic corrosion which occurs in the case of a copper terminal of the related art. However, in a case where an aluminum alloy is used for the terminal, strength and spring characteristics of the terminal per se are not sufficient. Further, in order to compensate for the above, a structure incorporating a spring made of an iron-based material in the terminal is employed, and thus there is a problem of galvanic corrosion between a spring member and a terminal base material (aluminum) and a problem of an increased production cost due to time and efforts required for assembling.
Japanese Patent No. 4598039 discloses a configuration in which, in order to protect a connection part between the electric wire and the terminal, a copper cap is attached to a portion of an aluminum wire where a conductor is exposed. However, there is a problem of an increased volume of a crimp portion due to an existence of the cap and a problem of a bad crimp connection and an increased production cost due to an increase in number of parts.
Further, in Japanese Laid-Open Patent Publication 2011-222243, a method of molding an entire crimp connection portion with a resin is employed, and there is a problem of an increased size of a connector housing due to an enlarged mold portion, which makes it difficult to make the entire wire harness with a high-density and miniaturized structure, and a problem that a process of manufacturing a wire harness and an operation thereof become more complicated. Japanese Laid-Open Patent Publication 2004-207172 discloses employing a method in which, in order to shield an aluminum conductor from outside, a metal cap is provided to cover the wire conductor and thereafter a crimp piece of the terminal metal fitting is further crimped. However, there is a problem that a process of attaching the aforementioned metal cap to each conductor before crimping the crimp piece of the terminal metal fitting is cumbersome and a problem of an immersion due to breakage of the metal cap by a wire barrel during crimping.
The aforementioned problem can be solved by employing a structure of a connecting portion to an electric wire in which an electric wire is inserted in to a tubular (bag-like) terminal and crimped to thereby shield an electric wire from outside without increasing the size of a crimp portion. Among several methods of forming a tube, it is preferable to employ a laser welding method (e.g., see Japanese Laid-Open Patent Publication 2003-191085) from the processing speed and the cost points of view, in addition to the point that the width of the weld portion can narrowed.
However, when the YAG laser welding method disclosed in patent document 5 is used, although a collecting beam diameter of a YAG laser is smaller than that of other welding methods, it is still considerably large from a practical point of view and the width of the weld portion becomes large. Therefore, when welded by YAG laser welding, there is a drawback that a molten portion is likely to fall, and, as a result, a wall thickness of the weld portion decreases.
In a terminal in which a tubular crimp portion is formed by using a copper alloy plate (metal member) having a coating layer such as a tin layer on its surface and by laser welding it, if a considerable amount of solid solution of Sn is produced in the weld portion, the strength of the weld portion becomes too high. When an electric wire is inserted into such a tubular crimp portion and crimped, the weld portion might break.
The present disclosure is contrived in view of the aforementioned drawbacks and it is an object of the present disclosure to provide a terminal having a weld portion that is preferably formed in a tubular crimp portion by laser welding. That is, a decrease in a strength and a decrease in a thickness of the weld portion are suppressed and cracking during the crimping process is suppressed. Also, it is an object of the present disclosure is to provide a wire connecting structure that includes such a terminal.